Advanced Sql

Jakub Romanowski

Free Course of the Month: 2023 Monthly SQL Practice Sets – Advanced

Enhance your SQL skills this June 2024 with our exclusive offer on the 2023 Monthly SQL Practice Sets - Advanced course, available for free for a limited time! As summer rolls in, it's the perfect time to learn new skills or brush up on the ones you've got. This June, why not seize the chance to deepen your SQL expertise with some challenging exercises drawn straight from the business world?

Tihomir Babic

15 Tricky SQL Interview Questions for Experienced Users

SQL interview questions for experienced users usually contain some trick(y) questions. Interviewers use them to test your gumption, which is typically a result of extensive experience and a high level of SQL knowledge.  I will show you 15 tricky SQL interview questions (mostly coding) in this article. Mind you, these are not necessarily complex questions. Actually, that’s their main characteristic: they seem very easy and straightforward, but that’s the interviewer trying to deceive you.

Ignacio L. Bisso

25 Advanced SQL Query Examples

One of the best ways to learn advanced SQL is by studying example queries. In this article, we'll show 25 examples of advanced SQL queries from medium to high complexity. You can use them to refresh your knowledge of advanced SQL or to review before a SQL interview. Many of the examples in this article will be based on the following employee table. Only a few examples will be based on other tables; in these cases, the tables will be explained along with the example.

Alexandre Bruffa

Learn Advanced SQL with LearnSQL.com

In this article, we will propose a learning path that will cover advanced SQL topics. If you already know the basics of SQL, you probably have figured out that most online and offline SQL tutorials and courses usually cover the basic and intermediate concepts: SELECT, FROM, WHERE, ORDER BY, GROUP BY, and joining tables. Even university database courses typically don’t cover more advanced  SQL topics. While this is enough SQL for most everyday tasks, there are some relatively new features that have been added to SQL in the last 20 years: window functions, recursive queries, and GROUP BY extensions (ROLLUP, CUBE, GROUPING SET).

Aldo Zelen

How to Become a Database Analyst

Curious about becoming a database analyst? Maybe you've taken some database courses at university and they really struck a chord. Or maybe you learned online. Now you're thinking about making a career out of working with databases. Where would you start? What should you expect at each phase of your professional development? In this post, we'll explore the challenging and exciting world of databases analysis. We'll go from the very beginning of a career to the apex of professional success.

Dejan Sarka

Statistics in SQL: Dependencies Between Discrete Variables

In my previous article, we looked at how you can calculate linear dependencies between two continuous variables with covariance and correlation. Both methods use the means of the two variables in their calculations. However, mean values and other population moments make no sense for categorical (nominal) variables. For instance, if you denote "Clerical" as 1 and "Professional" as 2 for an occupation variable, what does the average of 1.5 signify?

Aldo Zelen

Simplify SQL Code: Recursive Queries in DBMS

Hey SQL users! Are you repeating the same query in every report? Are your queries getting too complicated? Use recursive queries to simplify SQL code! Too many SQL reports can lead to clutter on your desktop and in your head. And is it really necessary to code each of them separately? Ad-hoc queries can share much of the same SQL code with managerial reports and even regulatory reports. Suppose you’ve been writing basic SQL code for a while.

Aldo Zelen

Common SQL Window Functions: Positional Functions

Positional SQL window functions deal with data's location in the set. In this post, we explain LEAD, LAG, and other positional functions. SQL window functions allow us to aggregate data while still using individual row values. We've already dealt with ranking functions and the use of partitions. In this post, we'll examine positional window functions, which are extremely helpful in reporting and summarizing data. Specifically, we'll look at LAG, LEAD, FIRST_VALUE and LAST_VALUE.

Aldo Zelen

SQL Window Functions: Partitions and Ranking Functions

You’ve started your mastery of SQL window functions by learning RANK, NTILE, and other basic functions. In this article, we will explain how to use SQL partitions with ranking functions. Mastering SQL window functions (AKA analytical functions) is a bumpy road, but it helps to break the journey into logical stages that build on each other. In the previous Common SQL Functions article, you learned about the various rank functions, which are the most basic form of window functions.

Ignacio L. Bisso

SQL Window Function Example With Explanations

Interested in how window functions work? Scroll down to see our SQL window function example with definitive explanations! SQL window functions are a bit different; they compute their result based on a set of rowsrather than on a single row. In fact, the “window” in “window function” refers to that set of rows. Window functions are similar to aggregate functions, but there is one important difference. When we use aggregate functions with the GROUP BY clause, we “lose” the individual rows.

Dejan Sarka

High Performance Statistical Queries – Skewness and Kurtosis

In descriptive statistics, the first four population moments include center, spread, skewness, and kurtosis or peakedness of a distribution. In this article, I am explaining the third and fourth population moments, the skewness and the kurtosis, and how to calculate them. Mean uses the values on the first degree in the calculation; therefore, it is the first population moment. Standard deviation uses the squared values and is therefore the second population moment.